Why do the slope rules for parallel or perpendicular lines indicate nonvertical lines only?
A.
The slope rules only indicate nonvertical lines because the slope of a vertical line is undefined, so it cannot be compared or multiplied.
C.
The slope rules only indicate nonvertical lines because vertical lines are perpendicular to all other lines.
D.
The slope rules only indicate nonvertical lines because vertical lines are never parallel to other lines.

Question

Why do the slope rules for parallel or perpendicular lines indicate nonvertical lines​ only?
A.
The slope rules only indicate nonvertical lines because the slope of a vertical line is​ undefined, so it cannot be compared or multiplied.
C.
The slope rules only indicate nonvertical lines because vertical lines are perpendicular to all other lines.
D.
The slope rules only indicate nonvertical lines because vertical lines are never parallel to other lines.

johnweldon1993 · Answer

Well we know slope is the change in y / change in x

So where we have a vertical line...

|dw:1473368377736:dw|

There is a change in y...but there is NO change in 'x'

So if you try and find the slope of that line and you put something like $\large slope = \frac{\Delta y}{\Delta x} =  \frac{5}{0}$ into your calculator...you wouldn't get an answer

Because we can not divide by 0...it is undefined